Video Texture Module Resolution?
When setting up the image source specify a capsize.

e.g.:

source.capsize = [50, 50]


Based on your code:

BGE 2.50+

setup

import bge

controller = bge.logic.getCurrentController()
owner = controller.owner

cameraName = owner['cam']
materialName = owner['material']

scene = bge.logic.getCurrentScene()
camera = scene.cameras[cameraName]

materialId = bge.texture.materialID(owner, "MA" + materialName)

renderToTexture = bge.texture.Texture(owner, materialId)
owner["RenderToTexture"] = renderToTexture

source = bge.texture.ImageRender(scene, camera)
source.capsize = [50, 50]
renderToTexture.source = source


refresh

import bge

controller = bge.logic.getCurrentController()
controller.owner["RenderToTexture"].refresh(True)




BGE 2.49

setup

import GameLogic
import VideoTexture

controller = GameLogic.getCurrentController()
owner = controller.owner

cameraName = owner['cam']
materialName = owner['material']

scene = GameLogic.getCurrentScene()
camera = scene.cameras["OB" + cameraName]

materialId = VideoTexture.materialID(owner, "MA" + materialName)

renderToTexture = VideoTexture.Texture(owner, materialId)
owner["RenderToTexture"] = renderToTexture

source = VideoTexture.ImageRender(scene, camera)
source.capsize = [50, 50]
renderToTexture.source = source


refresh

import GameLogic

controller = GameLogic.getCurrentController()
controller.owner["RenderToTexture"].refresh(True)